Method for enhancing optical properties in ceramics having applications in dental restorations

ABSTRACT

A method for enhancing optical properties of sintered, zirconia ceramic bodies and zirconia ceramic dental restorations is provided. The porous or pre-sintered stage of a ceramic body is treated with an yttrium-containing composition and sintered, resulting in sintered ceramic bodies having enhanced optical properties. The enhanced optical properties may be substantially permanent, remaining for the useful life of the sintered ceramic body.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of, and priority to, U.S.Provisional Patent Application No. 62/472,195, filed Mar. 16, 2017, andU.S. Provisional Patent Application No. 62/472,100, filed Mar. 16, 2017,the entireties of which applications are incorporated herein byreference.

BACKGROUND

Ceramic bodies that are colorized by known processes before or aftersintering show a decrease in translucency upon application of thecolorant. Post-sintering treatments to enhance a translucent effect areoften temporary, failing to last the useful life of the restoration.Other translucency enhancing treatments mimic enhanced translucencywithout actually increasing percent transmittance.

SUMMARY

A method for making highly translucent sintered ceramic bodies isprovided. The sintered ceramic bodies are suitable for use in dentalrestorations. Enhanced properties may be substantially permanent for theuseful life of the restoration. A method is provided for treating apre-sintered ceramic body with an yttrium-containing composition; aftersintering, the ceramic body has greater yttria concentration where theyttrium-containing composition was applied, and a higher percenttransmittance than an untreated ceramic body of the same ceramicmaterial. Sintered restorations made by the methods described hereinhave a color space (CIE L*a*b*) values within a desired range, and havesuitable strength in the final sintered ceramic dental restoration foruse in anterior and/or posterior dental applications. Thus, methods andcompositions are described for forming sintered ceramic dentalrestorations in selected shades that have enhanced translucency andsuitable strength.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1. Front view of an illustration of a dental restoration.

FIG. 2. Cross-sectional illustration of a dental restoration.

FIG. 3. Graphical representation of transmittance over a wavelengthrange.

FIG. 4. Graphical representation of transmittance over a wavelengthrange.

FIG. 5. Graphical representation of transmittance over a wavelengthrange.

FIG. 6. Graphical representation of transmittance over a wavelengthrange.

FIG. 7. Graphical representation of transmittance over a wavelengthrange.

FIG. 8. Graphical representation of transmittance over a wavelengthrange.

FIG. 9. Graphical representation of transmittance over a wavelengthrange.

DETAILED DESCRIPTION

With reference to FIG. 1, a method is provided for treating apre-sintered or bisque stage zirconia ceramic body, such as a dentalrestoration (100), by applying an yttrium-containing composition to thebisque ceramic body, and, then, sintering to approximately full density.The yttrium-containing composition comprises an yttrium-containingmaterial and, optionally, a colorant. In one embodiment, theyttrium-containing composition comprises an yttrium chloride aqueoussolution or sol, and one or more colorants. The treated, sinteredceramic body has a natural tooth shade and greater translucency than anuntreated, sintered ceramic body having a similar shade.

The yttrium-containing composition comprises an amount of anyttrium-containing material that is sufficient to impart hightransmittance in a sintered ceramic body, when tested according to themethods described herein. The yttrium-containing composition maycomprise approximately 5% by weight (wt %) to approximately 70% byweight of the yttrium-containing material, such as an yttrium salt,based on the total weight of the yttrium-containing composition. Inother embodiments, the amount of yttrium-containing material may bebetween 10 wt. % and 70 wt. %, based on the total weight of theyttrium-containing composition, or between approximately 20 wt. % and 70wt. %, or between approximately 30 wt. % and approximately 70 wt. %, orbetween approximately 40 wt. % and approximately 70 wt. %, or betweenapproximately 50 wt. % and approximately 70 wt. %, or betweenapproximately 20 wt. % and approximately 60 wt. %, or betweenapproximately 20 wt. % and approximately 65 wt. %, or betweenapproximately 20 wt. % and approximately 40 wt. %, or betweenapproximately 40 wt. % and approximately 60 wt. %, or betweenapproximately 50 wt. % and approximately 60 wt. %, based on the totalweight of the yttrium-containing composition. Yttrium-containingmaterials include, but are not limited to, yttrium salts, such asyttrium chloride, including yttrium chloride hexahydrate (e.g., yttrium(III) chloride hexahydrate), yttrium nitrate (e.g., yttrium (III)nitrate hexahydrate), and yttrium carbonate (e.g., yttrium (III)carbonate hydrate).

The one or more colorants of the yttrium-containing composition compriseat least one coloring agent that may be selected for example, to achievea specific lightness, hue or chroma value of the ceramic material in thefinal sintered body. The colorant may be selected to impart a shadesuitable for use in dental restorations, such as a shade based on anindustry-recognized shade guide, such as the VITA Classical Shade Guide.Colorants may include coloring agents and coloring liquids, described incommonly owned US Patent Publication Nos. 2013/0231239, 2014/0109797,and U.S. Pat. No. 9,095,403, each of which is incorporated by referenceherein in their entirety.

Colorants may comprise at least one coloring agent comprising ametal-containing component, including metallic compounds and metalliccomplexes. Metal-containing components may comprise metallic salts thatcontain transition metals from groups 3-14 on the periodic table, rareearth metals, and mixtures thereof. For example, coloring agents maycomprise metal-containing components in the form of oxides or salts ofmetals including but not limited to, iron, terbium, erbium, chromium,cobalt and manganese. Metal-containing components in the form of oxidesor salts may contain anions, including but not limited to C1⁻, SO₄ ²⁻,SO₃ ²⁻, Br⁻, F⁻, NO₂ ⁻, and NO₃ ⁻.

In one embodiment, the at least one metallic salt comprises one or moremetals selected from chromium, terbium, and manganese. Terbium, chromiumand manganese may be present as a form of terbium chloride, chromiumchloride, and manganese sulfate, respectively.

The at least one metallic salt may be added in an amount in the range ofapproximately 0.05 wt % to approximately 2 wt % metallic salt based onthe total weight of the yttrium-containing composition, or approximately0.07 wt % to approximately 1 wt % metallic salt based on the totalweight of the yttrium-containing composition. Alternatively, the amountof metallic salt is in a range of approximately 0.1 wt % to 0.5 wt %metallic salt based on the total weight of the yttrium-containingcomposition.

Coloring liquids to be incorporated into yttrium-containing compositionsmay be prepared as aqueous coloring solutions having no solid colorantparticles that are detectable at ambient temperature to the unaided eyeafter mixing a coloring agent with a solvent. Multiple coloring liquidsmay be prepared and incorporated with the yttria-containing compositionto provide a range of natural tooth shades, providing color to ceramicmaterials that are otherwise deemed to have an unacceptable shade ifused in dental applications in the uncolored stage. When coloringliquids are applied to a porous unshaded or porous shaded zirconiaceramic body, after sintering the colorized ceramic bodies may match,for example, a Vita Classical shade such as BL1, BL2, BL3, and BL4(bleach shades) and A1-D4 shades (e.g. A1, A2, A3, A3.5, A4, B1, B2, B3,B4, C1, C2, C3, C4, D2, D3, and D4) (e.g., from Vita Classical shadeguide).

Optionally, acids, such as citric acid may be added to increase thesolubility of the colorant, or the solubility of the yttrium-containingcomponent, or both the colorant and the yttrium-containing component.For example, an aqueous yttrium-containing composition may compriseapproximately 0.05M to approximately 5M citric acid, or fromapproximately 0.5M to approximately 5M citric acid, or fromapproximately 0.5M to approximately 2M citric acid. Organic solvent ornon-organic solvent may also be added to the liquid coloring solution orthe yttrium-containing composition, for example, to increase solubilityof the yttrium-containing material and/or coloring agents to reduce oreliminate visible particles.

In one embodiment, the yttrium-containing composition comprises anaqueous solution or sol of yttrium salt wherein the yttrium salt is inan amount between approximately 45 wt % and approximately 70 wt %, basedon the total weight of yttrium-containing composition, 0.05M to 5Mcitric acid, and a coloring agent comprising at least one metal oxide ormetal salt. In another embodiment, the yttrium-containing compositioncomprises an aqueous solution of yttrium salt in an amount betweenapproximately 60 wt % and approximately 70 wt %, based on the totalweight of yttrium-containing composition, 0.2M to 2M citric acid, and acoloring agent comprising at least one metal oxide or metal salt.

Yttrium-containing compositions are applied to green (unsintered)ceramic bodies, or pre-sintered ceramic bodies that that retain at leastpartial porosity for penetration of the yttrium-containing compositioninto the thickness of the material form.

Zirconia ceramic bodies comprise ceramic materials including, but notlimited to zirconia, partially stabilized or stabilized zirconia,including yttria-stabilized tetragonal zirconia, and mixtures thereof.Examples of partially stabilized or stabilized zirconia suitable for useherein include commercially available ceramic materials from Tosoh USA,such as zirconia that has been stabilized with yttria, (e.g., YSZzirconia from Tosoh) including approximately 0.1 mol % to approximately8 mol % yttria, or approximately 2 mol % to approximately 7 mol %yttria, or from approximately 2 mol % to approximately 6 mol % yttria,or from approximately 2 mol % to approximately 5 mol % yttria, or fromapproximately 3 mol % to approximately 5 mol % yttria, or fromapproximately 3 mol % yttria to approximately 4 mol % yttria, or fromapproximately 4 mol % yttria to approximately 5 mol % yttria, or fromapproximately 3.5 mol % yttria to approximately 5 mol % yttria. In oneembodiment, ceramic bodies are made from zirconia that has beenstabilized with approximately 1 mol % to approximately 3 mol % yttria.

Zirconia ceramic bodies may be made from ceramic materials that compriseapproximately 85 wt % to approximately 100 wt % zirconia or stabilizedzirconia, based on the total weight of the zirconia ceramic material, orapproximately 85 wt % or greater, or approximately 90 wt % or greater,or approximately 95 wt % or greater, or more than approximately 97 wt %or greater zirconia or stabilized zirconia, based on the total weight ofthe zirconia ceramic material. Other materials, such as, alumina mayalso be included in the zirconia ceramic material.

Zirconia ceramic bodies may be formed from zirconia powder having asubstantially uniform particle size distribution, such as powder with anaverage size in a range from approximately 0.005 micron (μm) toapproximately 1 μm. Examples of ceramic material suitable for use hereinalso include zirconia described in commonly owned U.S. Pat. No.8,298,329, which is hereby incorporated by reference in its entirety.

Ceramic powder may be made into a ceramic body shaped as a block, disk,near net shape, or a form that approximates the size and/or shape of asingle or multi-unit dental restoration, such as a crown, on-lay, bridgeincluding a multi-unit bridge comprising restorations having more thanone tooth structure, partial or full solid-body denture. Porous ceramicbodies may be made by processes including but not limited to uniaxial orbiaxial pressing or slip casting, and automated processes, includingadditive (e.g., 3-D printing) and subtractive (e.g., milling) automatedprocesses. Processes for making ceramic bodies suitable for use hereininclude those described in commonly owned U.S. Pat. Nos. 9,365,459,9,434,651, and 9,512,317, all of which are hereby incorporated in theirentirety, herein. Commercially available pre-sintered or bisque stateceramic bodies include those that have been heated to increase thedensity of a green body to below the full theoretical density of a fullysintered ceramic body in accordance with suggestions provided by themanufacturer. Pre-sintered ceramic bodies include those having a densityof approximately 30% to 90%, or approximately 50% to 90%, of fulltheoretical density.

The pre-sintered ceramic bodies may be shaped in the form of a dentalrestoration, such as a single unit crown, based on the individualrequirements of a patient, by milling or automated processes, includingCAD and/or CAM processes, prior to application of the yttrium-containingcomposition. Alternatively, the ceramic bodies may be sintered toapproximately full theoretical density after application of theyttrium-containing composition, prior to milling into a dentalrestoration by making a ceramic preform having a size and shape thataccommodates most custom restorations. Examples of suitable shaped formswhich may be sintered to full theoretical density prior to shaping to afinal dental restoration form may be found in commonly owned U.S. PatentPublication No. 2013/0316305, and U.S. Pat. Ser. No. D769, 449, both ofwhich are hereby incorporated herein in their entirety.

Pre-sintered, porous ceramic bodies may be made from unshaded(uncolored) or white ceramic powder. Alternatively, pre-colored ceramicpowders that are shaded to match a target or desired shade in a finalsintered body may be pressed or shaped into a porous body for usedherein, and include commercially available ceramic blocks, such asBruxZir® Shaded 16 series porous ceramic bodies (Glidewell Laboratories,Irvine, Calif.) that match the VITA Classic shades in a finalrestoration. Other pre-shaded ceramic powders are used for achieving arange of final dental shades in the sintered body, and the precisetarget shade is attained by additional coloring or staining before orafter sintering. Pre-shaded ceramic materials may advantageously provideuniform shade distribution throughout the sintered ceramic body

Colorants added to the yttrium-containing composition may be selected tomatch existing dentition, or to impart a natural or desired appearance,or to achieve a specific target shade (e.g., Vita Classical Shade Guideshade of, for example A1, or A2, or bleach shades.) To achieve a targetshade in a final restoration, the concentration of coloring agent addedto an yttrium-containing composition may be greater for ceramic bodiesmade from unshaded ceramic powder than ceramic bodies formed from ashaded ceramic powder, for a given target shade. Where the applicationof yttrium-containing composition has a lightening effect on a shadedceramic body, yttrium-containing compositions having lower weightpercent yttrium may require the addition of a lower weight percentcoloring agent to achieve a target shade.

Application techniques for applying the yttrium-containing compositionto penetrate the porous, pre-sintered ceramic bodies include, but arenot limited to, painting, dipping, spraying, or infiltrating the ceramicbody with the yttrium-containing composition by other known applicationmethods. In one embodiment, illustrated in FIG. 2, the cross-sectionalview of a shaped ceramic body in the form of a dental restoration, oneor more applications of the yttrium-containing composition may beapplied to one or more of the external buccal/labial (201), lingual(202), or distal or mesial, surfaces of a dental restoration form (200).The composition may be applied from the edge of the crown margin (101,205) area completely coating a restoration surface to the incisal orocclusal edge (together, may be referred to herein as biting edge forconvenience) (102, 203). Alternatively, the composition may be appliedonly to an area of the buccal or labial surface (which together, may bereferred to herein as facial surface for convenience) (103) that isvisible when the final sintered body is fitted in the mouth of apatient. In an embodiment, approximately one half to approximately onethird of a buccal or labial surface (104, 105) proximate the incisal orocclusal edge (biting edge) (102, 203) is treated, or alternately, onlythe tooth area that is visible upon sintering, is treated. In oneembodiment, the yttrium-containing composition may be applied to aninternal surface or cavity (204) of a dental restoration, specifically,an internal surface or cavity surface that abuts a tooth preparation forattachment in the mouth of a patient.

In another embodiment, pre-sintered ceramic bodies shaped as pre-formsor near net shapes may also be treated with the yttrium-containingcompositions. In one embodiment, the pre-form or near net shape may bedipped in a yttrium-containing composition to achieve partial orcomplete penetration through the thickness of a body in anotherembodiment, the yttrium-containing composition may be applied to one ormore sides or surfaces of a pre-form or near net shape that correspondswith an area that an occlusal or buccal surface of a restoration isultimately milled from the ceramic body. In this embodiment,pre-sintered ceramic bodies may be sintered after treatment with theyttrium-containing composition, prior to milling or grinding to form apatient-specific dental restoration.

In another embodiment, a second or subsequent application of the sameyttrium-containing composition may be applied to penetrate the porousceramic body before the first application that has penetrated the porousceramic body completely dries. Without wishing to be bound by theory, itis believed that in one embodiment, where a second or subsequentapplication applied to penetrate a portion of the porous ceramic bodythat comprises the first application of the yttrium-containing component(i.e., before the solvent of the first application dries), an edge ofthe region of the second application mixes or blends with a portion ofthe first application, and provides smooth transition between the firstand second application. The smooth transition between the first andsecond application may form a color and/or translucency gradient in afinal sintered body. In an alternate embodiment, a first application isapplied to a porous ceramic body and is dried (i.e., the solvent isremoved from the porous ceramic structure) before a second applicationis applied to only a portion of the first application. Where no mixingor blending of liquid compositions occurs at the edge of the secondapplication, a step-wise or layered shift in translucency or colorantmay result between the first and second application regions in the finalsintered body.

In one embodiment, a porous zirconia ceramic body in the form of adental restoration, such as a crown or a tooth-shaped form, may becompletely dipped to apply a second or subsequent coating of theyttrium-containing composition to the entire external and optionallyinternal surface of the dental form. In another embodiment, second orsubsequent application(s) are applied to a surface that is visible whenthe final sintered body is fitted in the mouth of a patient. Multipleapplication(s) of the yttrium-containing composition may be brushed orotherwise applied at the biting edge (e.g., incisal edge) (102),adjacent the biting surface, of the restoration for a distance ofapproximately 0.5 mm to approximately 3 mm, or for a distance ofapproximately 0.5 mm to approximately 4 mm, or for a distance ofapproximately 0.5 mm to approximately 5 mm, or for a distance ofapproximately 1 mm to approximately 5 mm, from the biting edge (102).For example, the yttrium-containing composition may be applied for adistance of approximately 1 mm, or approximately 1.5 mm, orapproximately 2 mm, or approximately 2.5 mm, or approximately 3 mm, fromthe biting edge. The yttrium-containing composition may be applied, forexample, by brushing in even or uneven patterns, such as a zigzagpattern or a jagged pattern in FIG. 1 (at 104, 105, 106). Optionally,one or more of the regions is applied by a technique that provides ajagged or zigzag edge between adjacent regions as seen in FIG. 1.Multiple applications of the yttrium-containing composition may resultin a sintered body having a first region (106) proximate the biting(e.g., incisal) edge (102) having a first concentration of yttria thatis greater than adjacent regions having a greater distance from thebiting edge, such as a second region (104), a third (105) region, andsubsequent regions (103), each of which may have increasingly lowerconcentrations of yttria as the distance from the biting (e.g., incisal)edge increases. In one embodiment, a method is provided for enhancingthe translucency of a porous zirconia ceramic body made of anyttria-stabilized zirconia material comprising 2 mol % yttria to 7 mol %yttria, wherein the method steps include applying an aqueousyttrium-containing composition comprising 20% wt to 70% wtyttrium-containing material and a colorant that comprises at least onemetal-containing component as a coloring agent. The method comprisesapplying a first application of the yttrium-containing composition topenetrate a portion of the porous zirconia ceramic body, and applying asecond application of the yttrium-containing composition to penetratethe portion of the porous zirconia ceramic body that comprises theaqueous yttrium-containing composition of the first application. In oneembodiment, the yttria-stabilized zirconia material is pre-shaded andthe yttrium-containing composition comprises between 40 wt % and 70 wt %of the yttrium-containing material. In another embodiment, theyttria-stabilized zirconia material is pre-shaded and comprises between3 mol % yttria and 5 mol % yttria, and the yttrium-containingcomposition comprises between 20 wt % and 40 wt % of anyttrium-chloride. In a further embodiment, the yttria-stabilizedzirconia material is an unshaded, white zirconia ceramic material andthe yttrium-containing composition comprises between 20 wt % and 65 wt %of the yttrium-containing material based on the total weight ofyttrium-containing composition. In one embodiment, the porous zirconiaceramic body is in the shape of a dental restoration having an incisaledge and a facial surface, and the method comprises applying a firstapplication of the yttrium-containing composition to the facial surfaceof the dental restoration from an incisal edge to a distance ofone-third to one-half the length of the facial surface proximate theincisal edge, and the second application penetrates a portion of theporous ceramic body that comprises the aqueous yttrium-containingcomposition from the first application. In a further embodiment, thefirst application is applied to the facial surface from the biting edgefor a first distance of 1 mm to 5 mm from the biting edge, and thesecond application is applied to the facial surface from the biting edgefor a second distance of 0.5 mm to 3 mm that is less than the firstdistance.

The yttrium-containing composition wets a porous ceramic body, forexample, by absorbing, infiltrating, diffusing, or otherwise penetratinginto the porous ceramic. Multiple applications may be applied to wetthrough the ceramic body to a specific depth, or through the entirethickness, or until no additional amount of the yttrium-containingcomposition absorbs or diffuses into the structure of the bisque stageceramic.

An application method for applying an yttria-containing composition toenhance optical properties of a sintered zirconia ceramic body, isprovided. In one embodiment, the method comprises applying a firstapplication of an aqueous yttria-containing composition to an edge of aporous ceramic dental restoration form comprising an yttria-stabilizedzirconia ceramic material for a first application distance of 1 mm to 5mm from the edge, and penetrating a portion of the porous body, whereinthe yttrium-containing composition comprises 30% wt to 70% wtyttrium-containing material and a colorant comprising at least onemetal-containing component as a coloring agent. The method furthercomprises applying a second application of the yttria-containingcomposition to the edge for a second application distance of 0.5 mm to 3mm from the edge, infiltrating a portion of the porous yttria-stabilizedzirconia ceramic body containing the aqueous yttria-containingcomposition from the first application, wherein the second distance isless than the first distance. The application method provides forenhanced translucency in the sintered dental restoration, for example,in the region proximate the incisal edge. The application method resultsin a transmittance of at least 46% or greater at 700 nm, when testedaccording to the method described herein as applied to a porous ceramicbody made from the yttria-stabilized zirconia ceramic material having a1 mm target thickness and sintered to at least 98% theoretical density.In one embodiment, the yttria-stabilized zirconia ceramic material is apre-shaded zirconia ceramic material, the yttrium-containing material is40% wt to 70% wt, and the application method provides at least 50% orgreater transmittance at 700 nm after sintering, when tested accordingto the method described herein as applied to a porous ceramic body madeof the pre-shaded zirconia ceramic material shaped to a target thicknessof 1 mm. In a further embodiment of the method, the yttria-stabilizedzirconia ceramic material is a pre-shaded zirconia ceramic material, theyttrium-containing material is 50% wt to 70% wt, and the applicationmethod results in at least 50% or greater transmittance at 700 nm aftersintering, when applied to a porous ceramic body comprising thepre-shaded zirconia ceramic material shaped to a target thickness of 1mm.

Sintered zirconia ceramic bodies reacted with a yttrium-containingcomposition, according to the methods described herein, have biaxialstrengths greater than or equal to approximately 500 MPA, greater thanor equal to approximately 600 MPA, or greater than or equal toapproximately 700 MPA, or greater than or equal to approximately 800MPA, or greater than or equal to approximately 900 MPa, when measuredaccording to the methods described herein. In one embodiment, a sinteredzirconia ceramic body having a biaxial strength greater than 800 MPa hasa natural dental restoration shade (Vita Classic Shade for dentalrestorations) and a percent transmittance (corrected, for samplethickness of 1 mm) that is greater than 45%, or greater than 46% orgreater than 47%, or greater than 48%, or greater than 50%, or greaterthan 52%, or greater than 53%. In one embodiment, the difference in themeasured percent transmittance between treated sintered zirconia bodiesand untreated sintered zirconia bodies (similarly prepared fromequivalent ceramic materials), is greater than 2% transmittance, orgreater than 3%, or greater than 4%, or greater than 5% transmittance,or greater than 7%, or greater than 9%, or greater than 10% (corrected;at 700 nm on a 1 mm thick sample). In some embodiments, the L valuechanges less than 6% or less than 5% or less than 3% in sintered ceramicbodies treated with an yttrium-containing composition compared tosimilarly prepare, untreated sintered ceramic bodies. In a furtherembodiment, translucency (percent transmittance at 700 nm) of treatedbodies increases while maintaining acceptable L*a*b values in the finalsintered body. In one embodiment, the difference in L* values (CIE colorspace) between an untreated sintered zirconia body and a treatedsintered zirconia body is less and or equal to 3%, or less than or equalto 2.5%. or less than or equal to 20%.

Test Methods

Density

The density strongly depends on the composition and structure of thesamples of the ceramic materials. Density calculations for ceramicbodies may be determined by liquid displacement method of Archimedesprinciple. Distilled water was used as the liquid medium. Density ofceramic samples were calculated using the following formula:

$\rho = \frac{( {W^{2} - W^{1}} )}{( {W^{4} - W^{1}} ) - ( {W^{3} - W^{2}} )}$

ρ=Density (gram/cc);

W1=Weight of empty specific gravity bottle (gram);

W2=Weight of specific gravity bottle with sample (gram);

W3=Weight of specific gravity bottle with sample and distill water(gram);

W4=Weight of specific gravity bottle with distill water (gram).

Flexural Strength Test

Flexure tests were performed on sintered test materials using theInstron-Flexural Strength Following ISO 6872 for preparation of strengthtesting for dental ceramic, flexural strength bar were milled andprepared. Once prepared, the bars were placed centrally on the bearersof the test machine so the load applied to a 4 mm wide face was along aline perpendicular to the long axis of the test piece. Then force isapplied and the load needed for breaking the test piece (loading ratewas 0.5 mm/min) was recorded. The flexural strength is calculated usingsample's dimensional parameter and critical load information.

Flexural strength, σ, in MPa was calculated according to the followingformula:

$\sigma = \frac{3\;{Pl}}{2\;{Wb}^{2}}$

where P is the breaking load, in newton; I is the test span(center-to-center distance between support rollers), in millimeters; wis the width of the specimen, i.e. the dimension of the side at rightangles to the direction of the applied load, in millimeters; b is thethickness of the specimen, i.e. the dimension of the side parallel tothe direction of the applied load, in millimeters. The mean and standarddeviation of the strength was reported. Test bars were prepared bycutting bisque materials taking into consideration the targeteddimensions of the sintered test bars and the enlargement factor (E. F.)of the material, as follows:

starting thickness=3 mm×E. F.;

starting width=4 mm×E. F.;

starting length=35 mm×E. F.

The cut, bisque bars were sintered and flexural strength data wasmeasured and calculated according to the 3 point flexural strength testdescribed in ISO (International Standard) 6872 Dentistry—CeramicMaterials.

Biaxial Strength Test (piston-on-three-ball test)

Universal mechanical testing machine, capable of a crosshead speed of 1mm/min (±0.5) and an ability to measure applied loads of between 10 Nand 2 500 N (±1%) was used.

The Biaxial flexural strength test fixture had a sample test support ofthree hardened steel balls with a diameter of (4.5±2) mm positioned 120°apart on a support circle with a diameter of (11±1) mm. The sample wasplaced concentrically on these supports and the load was applied with aflat punch with a diameter of (1.4±0.2) mm at the center of the samplespecimen. The experiment was conducted according to the test methoddescribed in ISO (International Standard) 6872 Dentistry—CeramicMaterials.

Translucency

Translucency was measured as percent transmittance. Sample wafers weresectioned from a bisque stage block and machined to a diameter thatapproximates a final diameter of approximately 30 mm after sintering.Wafers were ground flat until visually free of defects with 1200 and2000 grit SiC polishing paper. Surface dust was removed and the sampleswere sintered according to the sintering profile(s) described herein.The final thickness of the bisque body corresponded to a targetthickness of approximately 1.0 mm after sintering.

After sintering, sample wafers were briefly washed with isopropanol toremove errant surface material; however, no further surface preparationtechniques were applied to the samples prior to testing. Transmissionspectra were measured between the wavelengths of 360 nm to 740 nm with aKonica-Minolta CM5 spectrophotometer illuminated by a D65 light source.The spectrophotometer was calibrated to white and black prior tomeasurement. Translucency samples were placed flush against the(approximately) 24 mm integrating sphere aperture. A minimum of fourspectra were collected per sample and averaged to yield a finaltransmission spectra. Where noted, transmission spectra were correctedfor deviations in sample thickness.

Color Space (CIE. L*a*b*) Test

Zirconia materials were measured for color space according to CIE L*a*b*(International Commission on Illumination, measuring two polar axes forcolor, ‘a’ and ‘b’, and value (lightness, L)) values using a KonicaMinolta Spectrometer with a D65 light source.

27 mm×27 mm sintered test wafers were cut from pre-sintered bisqueblocks. The targeted final thickness of the test wafers after sinteringwas 1.0 mm. Therefore, the starting thickness for each wafer wascalculated based on the targeted final thickness taking intoconsideration the enlargement factor (EF) as follows:Final thickness×(EF)=bisque wafer thickness.

To measure color, the Konica Minolta Spectrometer was set on reflectancemode, and the L*a*b* values of the sample were measured. These valueswere referenced to materials made from traditional processes. Colorequivalence is indicated if a comparison of ceramic samples made by themethods described herein and traditional methods have a ΔE of less thanapproximately 3 or less, approximately 2.5 or less, or approximately 2or less.

Coloring Solutions

Coloring solutions were prepared according to the coloring solutionschart, and mixed in the yttrium-containing compositions, where indicatedin the Examples. Coloring solutions (1, 2 and 3) were selected thatprovided sintered zirconia ceramic bodies having shades that matchedcommonly requested shades from the Vita Classic shade guide, whenapplied to an unshaded, bisque body. Approximately 100 grams of acombination of terbium chloride hexahydrate and chromium chloride, andoptionally, manganese sulfate were added to form a coloring solution, asdescribed in Table 1.

TABLE 1 Coloring Solutions Chart. Solution 100 grams Propanediol WaterNo. Coloring agent (grams) (grams) Total salt (wt %) No. 1 TbCl3, CrCl3429.9 20698 0.47 No. 2 TbCl3, 449.4 21637 0.45 CrCl3 No. 3 TbCl3, 180.18670 1.12 CrCl3, MnSO4

Examples 1-6

Unshaded bisque stage zirconia ceramic bodies, treated withyttrium-containing compositions, were sintered and tested fortranslucency.

Sample wafers were milled from porous, pre-sintered unshaded BruxZir®zirconia milling blanks (unshaded, white 3YSZ) to target a thickness ofapproximately 1 mm after sintering.

Treatment compositions comprising yttrium chloride hexahydrate wereprepared in a range of concentrations from 10 wt % yttrium chloride(based on the total weight of the treatment composition) toapproximately 60 wt % yttrium chloride, as seen in Table 2. No coloringsolution was added. Yttrium chloride in water and propanediol were mixeduntil no more yttrium chloride was visible to the unaided eye, formingthe yttrium-containing treatment compositions.

The unshaded bisque zirconia wafers were dipped in theyttrium-containing treatment compositions for approximately 1 to 3minutes, and then dried, and sintered (substantially according tomanufacturer-provided instructions of the zirconia blocks) toapproximately full theoretical density.

Translucency measurements for treated and untreated unshaded 3 mol %yttria-stabilized zirconia ceramic bodies are shown in FIG. 3 and Table2, and compared to a control wafers of unshaded zirconia withoutdipping.

TABLE 2 Translucency (corrected, % Transmittance at 700 nm) of UnshadedZirconia (3YSZ) Dipped in Yttrium Chloride Compositions. % % YttriumChloride (Y) − Transmittance Example No. (no colorant) at 700 nmuntreated, unshaded 3YSZ — 51.4 control 1 10 wt % Y 51.5 7 20 wt % Y52.3 3 30 wt % Y 51.5 4 40 wt % Y 54.6 5 50 wt % Y 54.6; 57.3 {circlearound (1)} 6 60 wt % Y 55.9 {circle around (1)} Zirconia bisque stagesample dipped twice in 50% Yttrium chloride composition.

The difference between percent transmittance of ceramic bodies coatedwith yttrium-containing compositions comprising greater than or equal to40 wt % yttrium compared to untreated sintered ceramic body was greaterthan 3%, greater than 4%, and greater than 5%.

Examples 7-13

Unshaded zirconia bisque samples, treated with yttrium-containingcompositions comprising a colorant, were sintered and tested fortranslucency.

Sample wafers were prepared from porous, pre-sintered unshaded BruxZir®zirconia milling blanks (unshaded, white YSZ porous zirconia blanks, 3mol % yttria stabilized; Glidewell Laboratories, Irvine, Calif.) bymilling to a thickness of approximately 1 mm.

Treatment compositions comprising yttrium-chloride and No. 2 coloringsolution were prepared for a range of yttrium chloride concentrations inthe manner described above for Examples 1-6. No. 2 coloring solution wasprovided as described in Table 1, to which an amount of yttrium chloridewas added to achieve the approximate weight percent for the solution.Treatment compositions were prepared comprising from approximately 10 wt% yttrium chloride (based on the total weight of the treatmentcomposition) to approximately 60 wt % yttrium chloride, as seen in Table3. No. 2 colorant solution and yttrium chloride were mixed until theyttrium chloride was dissolved, or until no more yttrium chloride wasvisible to the unaided eye, forming the yttrium-containing treatmentcompositions.

Unshaded bisque zirconia wafers were dipped in the yttrium-containingtreatment compositions for approximately 1 to 3 minutes, and dried. Thesamples were sintered according to manufacturer-provided instructions toapproximately full theoretical density and tested as follows. Thesamples were compared to a control wafers of unshaded zirconia withoutthe application of the yttrium-containing composition, and dipped in No.2 coloring solution, only.

Translucency was measured for treated and untreated unshaded, 3 mol %yttria-stabilized zirconia ceramic bodies, as graphically shown in FIG.4 and reported in Table 3. Samples were compared to a control wafer thatwas not dipped in an yttrium-containing composition (3 mol %yttrium-containing composition, 3YSZ), and Ex. 7 which was dipped in thecoloring solution, but not the yttrium containing composition.

TABLE 3 Testing of Sintered Zirconia Bodies (white 3YSZ) Treated withYttrium Chloride Composition with Colorant (No. 2). Example Treatmentsolutions: % Transmittance at No. % yttrium chloride (Y) + color 700 nm3YSZ — 52.9 control 7 No. 2 coloring solution only 45.7 8 10 wt % Y +No. 2 color sol. 45.3 9 20 wt % Y + No. 2 color sol. 46.4 10 30 wt % Y +No. 2 color sol. 48.7 11 40 wt % Y + No. 2 color sol. 51.0 12 50 wt %Y + No. 2 color sol. 52.3 13 60 wt % Y + No. 2 color sol. 53.7

Samples dipped in yttrium-containing compositions greater than 10%yttrium formed sintered shaded ceramic bodies having a percenttransmittance greater than a sample dipped in coloring solution alone(Example 7). Samples dipped in yttrium-containing compositionscomprising coloring solution and yttrium of approximately 50% orgreater, upon sintering were shaded and had comparable or better percenttransmittance than the unshaded, untreated control (3YSZ control).

Examples 14-18

Porous, unshaded zirconia bisque samples were treated with anyttrium-containing composition comprising a colorant, sintered to fulldensity, and tested for translucency.

Unshaded zirconia ceramic blocks were obtained comprising 3 mol %yttria-stabilized zirconia (Glidewell Laboratories, Irvine, Calif.). Theporous bisque state blocks, and were milled to approximately a 1 mmthick sample size.

Multiple yttrium-containing solutions were prepared as described abovefor Examples 1-6, comprising from approximately 30 wt. %, approximately40 wt. %, approximately 50 wt. %, and approximately 60 wt. % yttriumchloride with the addition of an No. 3 coloring solution preparedaccording to Table 1. The samples were dipped in yttrium-containingsolutions for several minutes, and dried. The samples were sintered toapproximately full theoretical density according tomanufacturer-provided instructions.

The samples were tested for translucency, measured as percenttransmittance according to the methods provided herein, and the resultsare shown in FIG. 5. The percent transmittance at approximately 700 nmwas reported in Table 4.

TABLE 4 Translucency (% Transmittance at 700 nm) of Unshaded Zirconia(3YSZ) Samples Treated with Yttrium Chloride Compositions with Colorant(No. 3). % Yttrium Chloride (Y) + No. 3 Color % Transmittance ExampleNo. Sol. at 700 nm 14 coloring solution only 41.2 15 30 wt % Y + No. 3coloring sol. 41.2 16 40 wt % Y + No. 3 coloring sol. 44.3 17 50 wt %Y + No. 3 coloring sol. 48.1 18 60 wt % Y + No. 3 coloring sol. 50.1

Samples dipped in yttrium-containing compositions greater than or equalto 30% yttrium that comprised coloring solution, were sintered to formshaded ceramic that had greater percent transmittance than Example 14,which was dipped in coloring solution alone.

Examples 19-28

Shaded zirconia bisque samples treated with yttrium-containingcompositions comprising a colorant and without a colorant were sinteredand tested for translucency and strength.

Sample wafers were milled from porous, pre-sintered shaded BruxZir®milling blanks (Shade 100 zirconia mill blanks, 3YSZ; GlidewellLaboratories, Irvine, Calif.) to yield a thickness of approximately 1 mmafter sintering.

Treatment compositions comprising yttrium-chloride with and without. No.1 coloring solution were prepared comprising a range of yttrium chlorideconcentrations, as described above for Examples 1-6. No. 1 coloringsolution was provided as described in Table 1. Yttrium-containingcompositions without coloring solution (Table 5, FIG. 6) and with theaddition of coloring solution (Table 6, FIG. 7) were mixed inapproximate weight percentages (Tables 5 and 6) until no more yttriumchloride was visible to the unaided eye. Treatment compositions wereprepared in a range of concentrations, from approximately 30 wt %yttrium chloride (based on the total weight of the treatmentcomposition), and approximately 40 wt %, approximately 50 wt %,approximately 60 wt %, and approximately 65 wt % yttrium chloride, asseen in Tables 5 and 6.

Shaded bisque zirconia wafers were dipped in the yttrium-containingtreatment compositions (with and without coloring solution) forapproximately 1 to 3 minutes, and then dried. The samples were sinteredto full theoretical density. Samples were measured for percenttransmittance, as seen in FIG. 6 and FIG. 7, and reported (for 700 nmwavelength) in Table 5 and Table 6. Samples were compared to a controlwafers of shaded zirconia not dipped in a treatment composition (47.8%transmittance at 700 nm), and a control wafer (Ex. 23) dipped in No. 1solution with no yttrium chloride.

TABLE 5 Translucency (% Transmittance at 700 nm) of Shaded Zirconia(Shade 100 - 3YSZ) Dipped in Yttrium-Chloride Composition. % YttriumChloride (Y) − No % Transmittance Example No. colorant at 700 nm Shade100 — 47.8 untreated control 19 30 wt % Y 51.1 20 40 wt % Y 51.1 21 50wt % Y 52.1 22 60 wt % Y 53.1

Thus, zirconia bisque samples prepared from pre-shaded zirconia powder,that were dipped in yttrium-containing compositions greater than 30%yttrium and that comprised no coloring solution, were sintered to formceramic bodies having percent transmittance greater than the shaded,untreated zirconia standard (Shade 100 untreated).

TABLE 6 Translucency (% Transmittance at 700 nm) of Shaded Zirconia(Shade 100 - 3YSZ) Treated with Yttrium-Chloride Composition withColorant. % Yttrium Chloride + No. 1 Coloring % Transmittance ExampleNo. Sol. at 700 nm 23 coloring sol. only 48.0 24 30 wt % Y + No. 1coloring sol. 46.0 25 40 wt % Y + No. 1 coloring sol. 48.6 26 50 wt %Y + No. 1 coloring sol. 50.5 27 60 wt % Y + No. 1 coloring sol. 52.7 2865 wt % Y + No. 1 coloring sot. 51.5

Thus, zirconia bisque bodies made from shaded zirconia powder, and thendipped in yttrium-containing compositions (greater than 30% yttrium)that comprised coloring solution, had greater percent transmittance thanExample 23, which was a shaded bisque body dipped in coloring solutionalone (i.e. without yttrium-chloride).

TABLE 7 Comparison Table of Percent Transmittance of Sintered ZirconiaCeramic Bodies at 700 nm. Yttrium-containing Composition UnshadedZirconia. Shade 100 Zirconia (3YSZ) (3YSZ) Coloring Solution: % YttriumNo. 2 No. 3 No. 1 col. Chloride: no color col. Sol. col. Sol. no colorSol.  0 wt % YCl3 51.4 45.1 41.2 47.8 10 wt % YCl3 — — — 20 wt % YCl3 —— — 30 wt % YCl3 40 wt % YCl3 50 wt % YCl3 54.6 60 wt % YCl3 55.9 53.750.1 53.1 52.7

Shaded sintered ceramic made from unshaded 3YSZ samples that weretreated with yttrium-containing compositions having a colorant had thesame or greater translucency than untreated, uncolored white ceramicbodies, when the yttrium-containing composition comprised at leastapproximately 40 wt. % yttrium chloride or at least approximately 50 wt.% yttrium chloride, and a coloring solution for targeting an No. 2shade.

Sintered samples made from shaded 3YSZ (Shade 100) and treated withyttrium-containing compositions having at least 30 wt % yttriumchloride, had approximately the same or greater translucency thanuntreated, shaded ceramic bodies.

Examples 29-31

Zirconia ceramic bodies prepared with commercially availablecompositions were compared to both untreated zirconia ceramic bodies andzirconia ceramic bodies using compositions made according to the methodsprovided herein.

Sample wafers were milled from porous, pre-sintered unshaded BruxZir®milling blanks (unshaded, white porous, 3YSZ bisque blocks, commerciallyavailable as BruxZir® HT 2.0 blanks; Glidewell Laboratories, Irvine,Calif.) to a thickness of approximately 1 mm.

An yttrium-containing composition comprising 60 wt %. yttrium chloridein a 1M citric acid solution was prepared, as described above forExamples 1-6. No colorant was added. Commercially available liquidcompositions were obtained (Chang's Liquid—Old Translucency and YoungTranslucency; IDS CAD, Luray, Va.).

Sample wafers were coated by brushing with each composition in a similarmanner, and then dried. After sintering to approximately fulltheoretical density according to manufacturer-provided instructions,samples were tested for translucency. Transmittance was corrected forsample thickness, and may be seen in FIG. 8. At 700 nm, Example 29,zirconia ceramic body treated with 60 wt % yttrium chloride in 1M citricacid had a corrected transmittance of approximately 56%, and theuntreated zirconia ceramic body had a corrected transmittance ofapproximately 52%. Example 30 and 31, zirconia ceramic body treated withthe commercially available translucency enhancing liquids (OldTranslucency Effect and Young Translucency effect, respectively) had acorrected transmittance of approximately 42% and 34% transmittance at700 nm.

Examples 32-37

Shaded zirconia bisque samples treated with yttrium-containingcompositions comprising a colorant were sintered and tested fortranslucency (as percent transmittance).

Porous, pre-sintered 4 mol % yttria-stabilized zirconia blocks were madefrom powder (Tosoh USA) shaded to approximate the appearance of VitaClassical A2 in a sintered restoration. The blocks were pre-sintered toa bisque stage, and then, accommodating for shrinkage during sintering,bisque blocks were milled into the shape of wafers having a thicknessthat yields about a 1 mm thick wafer after sintering.

Treatment compositions comprising yttrium-chloride with No. 1 coloringsolution were prepared comprising a range of yttrium chlorideconcentrations. No. 1 coloring solution was provided as described inTable 1, and diluted to a concentration of approximately 33.3% wt.coloring solution. Yttrium-containing compositions were added to the33.3% No. 1 coloring solution in amounts to achieve between 10 wt % and50 wt % (Table 8), based on the total weight of the yttrium-containingcompositions and mixed until no more yttrium chloride was visible to theunaided eye. Bisque zirconia wafers were dipped in theyttrium-containing treatment compositions for approximately 1 to 3minutes, and then dried.

The samples of Examples 32-35 and Example 37 were sintered to fulltheoretical, according to the sintering profile, as follows: heating thesintering oven in which treated samples are placed from about 25° C. toabout 1200° C. in about 78 minutes, and having a dwell time of about 60minutes at 1200° C.; heating from about 1200° C. to about 1300° C. inabout 50 minutes; heating from about 1300° to about 1530° C. in about 28minutes, and having a dwell time of about 150 minutes at 1530° C.; andcooling the oven from about 1530° C. to about 155° C. in about 90minutes. Example 36 was sintered substantially similarly, except thatthe oven was heated from about 1300° C. to about 1500° C. in about 28minutes.

Samples were measured for percent transmittance, as seen in FIG. 9, andreported (for 700 nm wavelength, corrected for thickness) in Table 8.Samples were compared to a control wafers of shaded zirconia (4YSZ, inA2 target shade) that was not dipped in a treatment composition(approximately 50.0% transmittance at 700 nm).

TABLE 8 Translucency (% Transmittance at 700 nm) of Shaded Zirconia(4YSZ in A2 - equivalent Shade) Dipped in Yttrium-Chloride Composition.% Yttrium Chloride (Y) + % Transmittance Example No. No. 1 Colorant at700 nm 4YS - A2-Shade ceramic; — 50 untreated 32 10 wt % Y 50.6 33 20 wt% Y 51.7 34 30 wt % Y 51.7 35 40 wt % Y (1530° C.) 53.2 36 40 wt % Y(1500° C.) 54.4 37 50 wt % Y 48.0

Zirconia bisque samples prepared from pre-shaded zirconia powder thatwere dipped in compositions containing between 10 wt % yttrium and 40 wt% yttrium-containing composition comprising a coloring solution, weresintered to form ceramic bodies having percent transmittance greaterthan the shaded, untreated zirconia control (4YSZ, A2 target shade).

We claim:
 1. Method for enhancing the translucency of a sinteredzirconia dental restoration comprising obtaining a porous zirconiaceramic body that comprises an yttria-stabilized zirconia materialcomprising 2 mol % yttria to 7 mol % yttria, wherein the porous zirconiaceramic body is in the shape of a dental restoration having an incisaledge and a facial surface; obtaining an aqueous yttrium-containingcomposition comprising between 20% wt and 70% wt yttrium-containingmaterial, between 0.05M and 5M citric acid, and a colorant comprising atleast one metal-containing component as a coloring agent; and providinga first application of the yttrium-containing composition to penetrate aportion of the porous zirconia ceramic body; providing a secondapplication of the yttrium-containing composition to penetrate theportion of the porous zirconia ceramic body that comprises the aqueousyttrium-containing composition of the first application; and sinteringthe porous zirconia ceramic body after the first and second applicationto form a sintered zirconia dental restoration; wherein a difference inL* values (CIE color space) between (i) the sintered zirconia dentalrestoration having the first and second applications of theyttrium-containing composition and (ii) an untreated sintered zirconiadental restoration is less than or equal to 6%.
 2. The method of claim 1wherein the yttria-stabilized zirconia material is a pre-shaded zirconiaceramic material.
 3. The method of claim 1, wherein theyttria-stabilized zirconia material is a pre-shaded zirconia ceramicmaterial and the yttrium-containing composition comprises between 40 wt% and 70 wt % of the yttrium-containing material.
 4. The method of claim1, wherein the yttria-stabilized zirconia material is a pre-shadedzirconia ceramic material comprising from 3 mol % yttria to 5 mol %yttria, and the yttrium-containing composition comprises between 20 wt %and 40 wt % of an yttrium-chloride.
 5. The method of claim 1, whereinthe yttria-stabilized zirconia material is an unshaded, white zirconiaceramic material and the yttrium-containing composition comprises from20 wt % to 65 wt % of the yttrium-containing material based on the totalweight of yttrium-containing composition.
 6. The method of claim 1,wherein the at least one metal-containing component of the colorantcomprises one or more metals selected from terbium, erbium, chromium,cobalt and manganese.
 7. The method of claim 6, wherein the colorantcomprises one or more coloring agents selected from terbium chloride,chromium chloride, and manganese sulfate.
 8. The method of claim 1,wherein the colorant comprises 0.05 wt % to 2 wt % of a metallic salt asa coloring agent, based on the total weight of the yttrium-containingcomposition.
 9. The method of claim 1, wherein the porous zirconiaceramic body has a density of 50% to 90% of full theoretical density.10. The method of claim 1, wherein the yttria-stabilized zirconiaceramic material comprises 85 wt % to 100 wt % of a zirconia ceramicmaterial.
 11. The method of claim 1, comprising applying theyttrium-containing composition to the facial surface of the dentalrestoration from an incisal edge to a distance of one-third to one-halfthe length of the facial surface proximate the incisal edge, and theapplying the second application to penetrate a portion of the porousceramic body that comprises the aqueous yttrium-containing compositionfrom the first application.
 12. The method of claim 1, wherein the firstapplication is applied to the facial surface from the incisal edge for afirst distance of 1 mm to 5 mm from the incisal edge, and the secondapplication is applied to the facial surface from the incisal edge for asecond distance of 0.5 mm to 3 mm wherein the second distance is lessthan the first distance.
 13. The method of claim 1, further comprisingthe step of penetrating through the thickness of the ceramic body withthe yttrium-containing composition.
 14. The method of claim 1, whereinthe sintered body has an yttria concentration gradient wherein theyttria concentration is increasingly lower as the distance from theincisal edge increases.
 15. A method for applying an yttria-containingcomposition to enhance optical properties of a sintered zirconia ceramicbody, comprising an application method comprising applying a firstapplication of an aqueous yttria-containing composition to an edge of aporous ceramic dental restoration form comprising an yttria-stabilizedzirconia ceramic material for a first application distance of 1 mm to 5mm from the edge, and penetrating a portion of the porous ceramic dentalform, wherein the yttrium-containing composition comprises between 30%wt and 70% wt yttrium-containing material, between 0.05M and 5M citricacid, and a colorant comprising at least one metal-containing componentas a coloring agent; applying a second application of theyttria-containing composition to the edge for a second applicationdistance of 0.5 mm to 3 mm from the edge, penetrating the portion of theporous ceramic dental restoration form containing the aqueousyttria-containing composition from the first application, wherein thesecond application distance is less than the first application distance,wherein the application method provides at least 46% or greatertransmittance at 700 nm when applied to a porous zirconia ceramic bodymade from the yttria-stabilized zirconia ceramic material having a 1 mmtarget thickness when sintered to at least 98% theoretical density; andwherein a difference in L* values (CIE color space) between (i) asintered zirconia ceramic body having the first and second applicationsof the yttrium-containing composition and (ii) an untreated sinteredzirconia ceramic body is less than or equal to 6%; and sintering theporous ceramic dental restoration form after the first and secondapplication to form a dental restoration.
 16. The method of claim 15,wherein the porous, yttria-stabilized zirconia ceramic material is apre-shaded zirconia ceramic material, the yttrium-containing material isbetween 40% wt and 70% wt, and the application method provides at least50% or greater transmittance at 700 nm after sintering, when applied tothe porous zirconia ceramic body made from the yttria-stabilizedzirconia ceramic material shaped to a target thickness of 1 mm whensintered.
 17. The method of claim 15, wherein the porous,yttria-stabilized zirconia ceramic material is a pre-shaded zirconiaceramic material, the yttrium-containing material is between 50% wt and70% wt, and the application method results in at least 50% or greatertransmittance at 700 nm after sintering, when applied to the porouszirconia ceramic body made from the yttria-stabilized zirconia ceramicmaterial shaped to a target thickness of 1 mm when sintered.
 18. Methodfor enhancing the translucency of a sintered zirconia dental restorationcomprising obtaining a porous zirconia ceramic body formed from anyttria-stabilized zirconia powder comprising 2 mol % yttria to 5 mol %yttria, wherein the porous zirconia ceramic body is in the shape of adental restoration; obtaining an yttrium-containing compositioncomprising between 20 wt % and 70 wt % of an yttrium salt dissolved inan aqueous solvent, between 0.05M and 5M citric acid, and a colorantcomprising at least one metal-containing component as a coloring agent;and providing a first application of the yttrium-containing compositionto penetrate a portion of the porous zirconia ceramic body; providing asecond application of the yttrium-containing composition to penetratethe portion of the porous zirconia ceramic body that comprises theyttrium-containing composition of the first application; and sinteringthe porous zirconia ceramic body after the first and second applicationsto form a sintered zirconia dental restoration; wherein a difference inL* values (CIE color space) between (i) a sintered zirconia ceramic bodyhaving the first and second applications of the yttrium-containingcomposition and (ii) an untreated sintered zirconia ceramic body is lessthan or equal to 6%.
 19. The method of claim 18, wherein theyttrium-containing composition is applied to a facial surface adjacent abiting edge of the porous zirconia ceramic body.
 20. The method of claim18, wherein the yttrium salt comprises at least one of yttrium chloride,yttrium nitrate or yttrium carbonate.
 21. The method of claim 18,wherein the yttrium-containing composition comprises between 40 wt % and70 wt % yttrium salt dissolved in the aqueous solvent.
 22. The method ofclaim 18, wherein the yttrium-containing composition comprises between20 wt % and 65 wt % yttrium salt dissolved in the aqueous solvent. 23.The method of claim 18, wherein the yttrium-containing compositioncomprises between 40 wt % and 60 wt % yttrium salt dissolved in theaqueous solvent.
 24. The method of claim 18, wherein theyttria-stabilized zirconia powder comprises 3 mol % yttria to 5 mol %yttria.
 25. The method of claim 18, wherein the coloring agent comprisesat least one metallic salt, and the coloring agent provides a dentalshade to the porous zirconia ceramic body after sintering.
 26. Themethod of claim 25, wherein the yttrium-containing composition comprises0.05 wt % to 2 wt % of the at least one metallic salt, based on thetotal weight of the yttrium-containing composition.
 27. The method ofclaim 18, wherein the porous zirconia ceramic body is formed from anunshaded, white yttria-stabilized zirconia powder.
 28. The method ofclaim 18, wherein the yttria-stabilized zirconia powder comprises ashaded zirconia ceramic powder that provides a dental shade to theporous zirconia ceramic body after sintering.